Strain gauge transducers are conventionally utilized to sense loading such as is necessary in testing to make sure the components tested can withstand the stress involved during normal use and extraordinary loading. Usually such transducers are utilized to test the stress at joints and comprise bolts that hold the joints together. These bolt transducers are provided with strain gauges to sense the stress to which the joints are subjected. Certain strain gauge bolt transducers are provided with a portion having a square cross section on which strain gauges are mounted externally on each of the four sides to sense loading. Other strain gauge bolt transducers include a central hole of a round cross section defined by a round surface on which strain gauges are mounted internally to sense the loading. With the external type of bolt transducer, it is not possible to check the strain gauges without removing the bolts and thus breaking the joint connected by the bolt. With the internal type of bolt transducer, no checking of the strain gauges is ever possible due to the mounting thereof within the interior of the bolt hole. Furthermore, the strain gauges of both the external and internal type of bolt transducers are spaced relatively far from the central neutral axis of bending such that large error can be introduced in the load sensed during bending due to small gauge misalignment.
The United States patent of Wakeland et al 2,925,576 discloses a strain-sensitive electrical pick-up device which includes a columnar element having a threaded inner end that is received by a threaded hole and also having a flange that is seated about the hole. An intermediate portion of the element has a round shape and is wound by a strain wire to sense loading. This strain wire is located remote from the central axis of the element and is, therefore, subjected to reading bending error as the element is loaded.
The United States patent of Reichow et al 4,042,049 discloses load transducers including curved bending beams having curved faces on which associated pairs of strain gauges are mounted to sense loading. At opposite ends of the beams, mounts are provided to support the beams in position for sensing a load on a member being tested.
The U.S. Pat. No. 4,200,855 of Gilcher discloses a bolt-like railway vehicle wheel detector. This detector includes a strain gauge sensor having an intermediate surface on which a strain gauge is mounted to sense loading as a wheel of a rail car passes over a rail on which the sensor is mounted.
Other strain gauge transducers and load sensing devices are disclosed by the following U.S. Pat. Nos.: 2,393,714; 2,600,029; 2,747,454; 2,873,341; 3,132,319; 3,212,325; 3,905,356; and 4,127,788.